1. Field of the Invention
The present invention relates to an insert molding method and a metal mold therefor, that are used for molding a synthetic resin or rubber (hereinafter called xe2x80x9cinsert moldingxe2x80x9d) in a state where an insert (a work) is disposed in advance in a metal mold.
2. Description of the Prior Art
The insert molding is a method for injection molding of synthetic resin, etc., in a state where a pre-molded article called an insert or a work is disposed in advance in a molding metal mold, and forming a resin molding part on the upper surface and circumferential side of the insert. The insert molding has been widely utilized in production of various types of electronic components. Also, the insert molding is applicable to various types of resin molding methods. However, the present invention is limited to an injection molding method.
An insert disposed in a metal mold may be a resin molded component (plate-shaped, bar-shaped, or box-shaped, or of other shapes) that has already been processed, or a component made of a different type of material such as metal, glass, ceramic, carbon, etc.
There are many cases where the inserts are not necessarily accurately produced with respect to dimensional standards, for example, if an insert that is uneven in the thickness dimension thereof is disposed in a metal mold and injection molding is carried out, a gap is produced on the contacting surface between a part of the insert and the upper mold even if the molds are tightened, and injected resin is caused to flow out through the part to become burrs.
A detailed description thereof is given with reference to the accompanying drawings. As shown in FIG. 6-A, in a case where an insert 1 is plate-shaped, its finishing accuracy thereof is not satisfactory, and a difference of h1 less than h2 is produced with respect to the thickness thereof, the insert 1 is set on the upper surface of the lower mold 2 and the molds are tightened, wherein the side having a larger thickness (the h2 side) on the upper surface of the insert 1 is brought into contact with the underside of the upper mold 3, and clearance is produced at the side (the h1 side) having a smaller thickness. Speaking in a different way, since the insert 1 is inclined, clearance is produced at the circumference of the lower surface of a cavity 4 (recess) prepared on the upper mold 3 side. The cavity 4 is a part that is molded with a synthetic resin. Therefore, if synthetic resin is injected through a gate 5 in a state such clearance is produced below the circumference of the lower surface of the cavity 4, burrs 7 are produced at the lower end part of a resin molded component 6 as shown in FIG. 6-B.
Particularly, since resin is injected at a high-pressure level in the injection molding method, resin may leak through remarkably minute clearance or gaps and burrs are likely to occur. In order to prevent burrs from being produced, if the injection pressure is set to a lower level, inconveniences are brought about in accuracy and physical properties of the molded articles.
Several attempts have already been made in regard to improvement in preventing the above-described burrs from being produced in the insert molding. The result was disclosed in, for example, Japanese Unexamined Patent Publication No. Hei-8-288326, etc.
A problem regarding generation of burrs in the insert molding is a critical defect resulting in defective or useless insert products. Also, the problem results in an increase in production costs due to the occurrence of a necessity to remove burrs in addition to generation of production losses. It is therefore an urgent matter to solve such a problem.
The above-described Japanese Unexamined Patent Publication No. Hei-8-288326 described prevention of burrs from occurring by absorbing unevenness in insert thickness by supporting the underside of a supporting member on which an insert is placed by means of a resilient member (a plurality of string-wound springs) However, since the dimensional unevenness of inserts are not fixed but include various levels in unevenness, a completely satisfactory solution could not be achieved by supporting the inserts by a plurality of springs by which a uniform force is applied to the supporting member of the inserts.
In addition, as described above, there are a great many types of inserts, for example, not only metal inserts that are press-worked, and synthetic resin inserts, but also ceramic, carbon, and glass inserts that are likely to be broken with only a low impact force. In particular, in the case of the latter ones, which are uneven in terms of the outer dimensional evenness, there arise cases where the inserts disposed in the mold are broken when tightening the molds, thereby resulting in losses in products.
The present applicant disclosed an insert molding method and a metal mold, which are excellent in prevention of the above inserts from being broken, prevention of burrs from occurring, and production, operation and maintenance at metal molds, with Japanese Patent Application No. 2000-149547.
The insert molding method (metal mold for insert molding) according to the above-described preceding invention is an insert molding method (a metal mold for insert molding) for injection molding of resin or rubber at an insert set in a lower mold by injecting and filling melted resin or rubber into a cavity of an upper mold through a gate in a state where the upper mold and lower mold are disposed so as to be opposed to each other, wherein a movable supporting member for setting the above-described insert is inserted into and placed in a recess formed on the upper surface of the above-described lower mold, the position of the center of gravity on the underside of the movable supporting member is supported by the tip end of a shaft of a pressing mechanism and is pressed to the upper mold side, and the above-described movable supporting member is inclined centering around the pressing and supporting point by the corresponding shafts in the above-described recess so that, by causing a gap to exist between the side portion of the above-described recess and the side of the movable supporting member, the upper surface of the insert is evenly brought into surface contact with the underside of the upper mold.
As has been made clear in the above description, the preceding invention was constructed so that the position of the center of gravity of the underside of the movable supporting member is pressed in the direction of the upper mold by shafts of a single pressing means. Through subsequent study and research, such information was obtained, such as it being difficult to secure a balance of the movable supporting member with single-point supporting of the position of the center of gravity on the lower surface of the movable supporting member in a case where a molding article is large with its side exceeding, for example, 15 cm, or where an insert itself is large (for example, one side thereof exceeds approximately 20 cm). That is, in the case of insert molding of such a large-sized molding article or by such a large-sized insert, it was found that, with control made by single-point supporting of the movable supporting member, it was difficult to carry out stabilized injection molding in which no burrs are produced.
As has been made clear in the above description, it is therefore an object of the present invention to provide an insert molding method and a metal mold, which are capable of carrying out stabilized insert molding, in which no burrs are produced, even in insert molding of a large-sized molding article or by a large-sized insert.